Lens applicator for localized microwave hyperthermia

Hyperthermia is now recognized as an effective means for cancer therapy, and many reports on the irradiation of biological subjects by electromagnetic waves to produce dielectric heating and hyperthermia have been reported. Although it is desirable in hyperthermia selectively to heat the cancer tissue, it is difficult to estimate the heat distribution in the subject owing to insufficient analysis of the electromagnetic field distribution in the irradiated subject. At present it is not yet possible to control the temperature distribution in the biological subject. In electromagnetic wave hyperthermia, microwaves are effective from the viewpoint of efficiency or selective heating. On the other hand, it is difficult to heat a cancer in deep tissue because of reduced penetration of the microwaves into the subject. This paper shows experimentally and by theoretical analysis, using a microwave lens geometrically designed to produce a focused cylindrical wave as the applicator, that selective heating is possible for tissue 10 to 40 percent deeper than with planar wave. It is shown that the microwave lens applicator is effective for the heating of biological tissues.